In the food industry, liquids or beverages have to be deoxygenated in order to avoid any oxidation reactions or microbial growth which might take place during storage of the product. Leaving traces of oxygen in liquid foods, beverages, or pharmaceutical liquids reduces significantly their shelf-life and leads to early spoilage of the product. Therefore, liquid foods, beverages or pharmaceutical liquds are deoxygenated or are renderd inert before the final packaging or bottling operations. The deoxygenation step is usually performed in a holding tank where an inert gas such as N.sub.2 will strip away the dissolved oxygen when sparged through the liquid food.
However, during the filling stage of the final container, the deoxygenated liquid or beverage comes in contact with ambient air present in the container, particularly when this container has not been rendered inert. Leaving residual air in the headspace of the container after completion of the filling operation results in a transfer of the oxygen present in this headspace back into the liquid. Therefore, a major concern in the food industry is to develop a technique allowing purging of the headspace of the filled container with an inert gas before sealing or placing a lid on it. The residual partial pressure of oxygen in the headspace should usually not exceed 0.5%.
In the beer industry where the presence of oxygen in the headspace of the containers is particularly undesirable, the remaining air is purged via a step where the product is made to foam. Once transferred from the holding tank into the container, the beer is often made to foam by the introduction of a brief and pressurized jet of water. The resulting desorption of dissolved CO.sub.2 from the beer creates the foam which rises and flows out of the bottleneck. Such an operation is sufficient to purge the air from the container headspace and to replace it with CO.sub.2, but it leads to considerable losses of the contained product (between 1% and 5% of the final volume of that liquid).
In order to avoid the foaming step and the resulting loss of the product, solutions which consist of flushing out the air from the container's headspace with an inert gas, such as N.sub.2 or CO.sub.2, have been used, but did not yet succeed in lowering the residual O.sub.2 partial pressure in the headspace to a value less than 0.5%. In addition, the volume of gas required for the flushing operation may be high. Therefore, there has not been any satisfactory solution proposed to remove the oxygen from the headspace of liquid food or beverage containers after filling.
Certain chemical products are known to be obygen scavengers or absorbers as for example those disclosed in U.S. Pat. No. 4,113,652 ,4,104,192, 4,199,472, 4,127,503, 4,166,807, 4,192,773. All these and further patents are incorporated herein as references . Such products, like active iron oxides are react, in the presence of moisture, with gaseous oxygen to form iron oxides and hydroxides: EQU Fe(OH).sub.2 +1/4O.sub.2 +1/2H.sub.2 O--Fe(OH).sub.3
In other words, ferrous {Fe.sup.+2 ] hydroxide in the presence of moisture with gaseous oxygen reacts to form ferric {Fe.sup.+3 ] hydroxide.
Such chemicals are already widely used for the preservation of fresh, packed or prepared foods to remove the residual oxygen from the container and to extend the shelf-life of the product. In a common practice, these chemicals are wrapped in a permeable sachet which allws the permeation of oxygen and water vapor, while avoiding direct contact between the absorber and food. However, the presence of liquid in direct contact with the sachet is to be avoided since this creates a limitation of the permeation of the gas through the sachet. On the other hand, the direct contact of the liquid food with these chemicals is not recommended.
U.S. Pat. No. 4,332,845, 4,366,179 and 4,399,161 disclose some possible use of the above mentionned oxygen absorbers or scavengers. U.S. Pat. No. 4,399,161 discloses a method of storing a dewatered solid food in a gas tight packaging with oxygen absorbing means in a gas permeable package not suitable to avoid liquid contact with said absorber means. Furthermore, said solid food is packaged in a plastic tray before being packed in the air tight packaging, the oxygen absorber means being, in its own package, provided between these two envelopes. As described in U.S. Pat. No. 4,332,845, the product cannot be used with a liquid food or pharmaceutical packaging system for the following reasons : an oxygen absorber placed in a sealed bag is inappropriate for the removal of oxygen contained in the gaseous headspace of a container if immersed in the liquid food or pharmaceutical contained in the container. Therefore, the bag has to be placed and maintained in the headspace of the container. Such a requiement is impossible to achieve in the case of an automatic filling line unless the time between filling and lidding or sealing steps is considerably extended. If such is the case, the productivity of the line is significantly reduced. On the other hand, considering the shape or geometry of commercial liquid containers used with automatic filling lines, an oxygen absorber placed within a bag cannot be placed and maintained in the headspace of the container.